Who Dies When the World Catches the Flu?

"[In 1918], the poorer the country, the higher the mortality from the flu," Murray said. There was more than a 30-fold variation in mortality between countries they noted.

The researchers say the situation would be the same today.

This highlights the fact that despite medical advances, the disparities in health between rich and poor countries continues to remain extremely high, experts said. The poor continue to not benefit much from the increased wealth and advancements that the rest of the world is seeing.

"There are two main reasons why the poorer countries have a greater proportion of the deaths," Hill said. "One is that the health infrastructure is weaker in developing countries. And the second is that the populations are less healthy to begin with."

"Due to poor nutrition and other diseases the poor are more easily compromised."

Other experts agree that given the conditions in which many in the developing countries live -- where there is overcrowding and limited or no access to simple things like clean drinking water -- it is not surprising to see such a stark contrast.

U.S. Would Not Be Safe

While the United States has a detailed pandemic preparedness plan, the researchers say it will not be able to avoid a pandemic if one were to occur.

"We have the ability to monitor new strains of influenza and create vaccines, which may be of help, but we cannot completely protect ourselves in that way," Hill said. "The thing about influenza virus is that it is extremely contagious. It is hard to control if it gets into the human population."

"The 1918 influenza spread around in a matter of weeks even without air traffic. Attempts to seal off borders don't work," Hill said.

While the 1918 pandemic is a worst-case scenario, there is no guarantee that the next pandemic will not be even more deadly. And experts agree that one of the best ways to prevent the deaths from such a virus would be to make sure that developing countries are better prepared to handle a pandemic.

"Developed countries have an obligation to protect the population of developing countries," Hill said.

"In many ways there hasn't been enough focus on helping poor countries to have practical strategies to prepare for the flu," Murray said. "Because most of the mortality will be in poor countries, we need to focus more policy attention in helping them in coming up with effective strategies."